In recent times, there has been a notable increase in the attention and implementation of top solutions for residential solar energy solar energy systems, driven by the growing emphasis on sustainability and the need to address climate change. The adoption of renewable energy sources is of paramount importance in addressing the complex issues presented by climate change, and household solar power assumes a substantial role in facilitating this transition. This article focuses on Littelfuse’s solutions for residential solar systems and their crucial contribution to the establishment of a net-zero future.
Residential solar inverters
Estimates for the home solar inverter market indicate a healthy growth rate of 10.9% from 2023 to 2032, from an initial valuation of $6.95 billion in 2023. Effective energy utilization rules, changing consumer and regulatory inclinations toward solar power, and other factors have all contributed to the acceleration of solar technology adoption.
In residential applications, three main types of solar inverters are used (Figure 1):
- Microinverter: In this system, the single-phase DC/AC power conversion is performed at the panel level, achieving output power up to 300 W in the 110- to 230-V range. Power optimization is performed locally on each panel, and AC-coupled batteries can be added for backup.
- String inverter: Achieving 1-kW to 10-kW output power and available with both single-phase and three-phase output voltage, this system has centralized DC/AC conversion. Known for their availability and reliability, string inverters simplify maintenance, as no electronics are installed on the roof. Battery backup can be high-voltage DC-coupled.
- Power optimizer + string inverter: Like the string inverter, this system has a centralized power conversion and high-voltage DC-coupled battery backup. Here, however, the output power of each panel is optimized independently, and both system- and panel-level monitoring are provided. The rated output power can be up to 300 W, with each panel providing a 50-VDC output voltage.
Littelfuse encompasses a broad range of products and solutions meeting the requirements of the solar inverters installed in residential systems, including input and output protections, power conversion devices and components for implementing the user interface and communicating with the grid (Figure 2).
Microinverter
The typical schematic of a microinverter is shown in Figure 3. After the solar panel, we have a DC/DC converter (Block I), followed by a high-frequency transformer and a full-wave rectifier stage (II). After the DC/DC converter, we have a DC/AC inverter (III) and an output stage with filters and protections (IV), used to interface with the grid and the AC-coupled battery system. The gate driver ICs (V) complete the power section.
At the bottom of Figure 3, we see the control unit, which includes the auxiliary power supply (VII), usually powered by the solar panel, a microcontroller, and a communication and user interface (VI). As shown in the table of Figure 3, Littelfuse’s products are suitable for implementing each block of the microinverter.
The Trench Gate Gen2, for instance, is a 40- to 175-V power MOSFET with VDS ratings from 40 V to 170 V and providing high-current capabilities of up to 600 A. Designers can control more power with less space required thanks to the combination of these devices’ high-current ratings and accessible compact packaging alternatives. Additionally, these devices enhance device consolidation by minimizing or eliminating the need for numerous paralleled MOSFET devices with lower current ratings in high-power-switching applications.
Power optimizer
At a voltage determined by the inverter, power optimizers track each input’s maximum power point and send all available power to the output. Doing so does not necessitate any sort of interaction between the optimizers and inverter. Keep in mind that not all PV systems that rely on string inverters will include power optimizers.
The block diagram of the power optimizer is shown in Figure 4, where each vertical block can be repeated n times. For the buck or boost DC/DC converter, high-frequency switching MOSFETs, TVS diodes to protect the MOSFETs from voltage transients, and NTC to detect high temperatures caused by excessive sunlight or power component failures are required. The gate drivers control the switching MOSFETs and are combined with TVS diodes to protect the device from transient overload events. To protect the control unit, which integrates programmable logic devices and communication interfaces, from electrostatic discharge (ESD) and electrical fast transients (EFTs), TVS diode arrays are normally employed.
The table on the right of Figure 4 shows a selection of Littelfuse solutions suitable for this application. For instance, to prevent damage from ESD, EFTs and surges caused by lightning, the SP712 TVS Diode Array is specifically intended to safeguard RS-485 applications with asymmetrical working voltages (–7 V to 12 V). Safely dissipating up to 20 A of 8/20-µs generated surge current (IEC 61000-4-5) with very low clamping voltages, the SP712 can withstand repeated ESD strikes above the maximum level stipulated in IEC 61000-4-2 without deteriorating performance.
String inverter
Even though there are several topologies including string inverters, for the sake of simplicity, we will consider the basic one. The block diagram of the string inverter system is shown in Figure 5. The string inverter block includes the control unit that, besides wired connections, might also include wireless interfaces, such as BLE, Zigbee and more.
The solar panels are connected to the input of the string inverter block via input protection and filters. Metal oxide varistors (MOVs) are normally used for this purpose, protecting from voltage transients and lighting surges. The Littelfuse SM20 series are compact (20 mm) SMD varistors for use in applications like this, requiring high-energy and transient-current capability.
Similarly, filters and protections composed of MOVs, fuses and gas discharge tubes are placed at the output of the string inverter. High-isolation and surge-protection applications like this, as well as those involving bias voltages or signal levels of several hundred volts, are ideal for the Littelfuse CG3 family of gas plasma arresters, which have two terminals and operate at voltages ranging from 1.0 to 7.5 kV.
The use of renewable energy sources is a crucial approach in the pressing effort to address climate change. Residential solar energy stands out as a promising solution, as it not only provides sustainable power generation but also enables individuals to actively engage in the challenge of reducing carbon emissions. In the pursuit of decarbonization, the use of efficient, reliable and compact solutions in domestic solar energy facilitates the generation of environmentally friendly and sustainable electricity.
